Laminated safety glass consists of two lites of glass joined by an energy absorbing plastic interlayer, typically polyvinylbutyral (PVB). Laminated safety glass is used in automotive windshields and in architectural building glass. Architects are continually using glass in more demanding applications such as balustrades, partitions, floors, doors, and overhead bolted glass. Laminated safety glass using plasticized PVB as the interlayer typically does not meet the strength or post glass breakage requirements for these applications. Ionomers of ethylene/methyacrylic acid copolymers (sold under the DuPont tradename Surlyn®) yield interlayer materials that are rigid, much stiffer and tougher than traditional PVB interlayers. Laminated safety glass utilizing stiffer, tougher interlayer has been shown to possess the strength and post glass breakage requirements needed for these demanding architectural applications.
In addition, it has been found that interlayers of ionomeric ethylene/methyacrylic acid copolymers demonstrate much improved edge stability over traditional PVB interlayers. This improved edge stability allows for laminated glass (with interlayers of ionomeric ethylene/methyacrylic acid copolymers) to be used in applications such as shower doors and exterior open edge applications where traditional laminated glass (with PVB interlayers) would not be used. In many of these above-mentioned applications (balustrades, partitions, floors, doors, overhead bolted glass, and shower doors) it would be desirable to have a decorative image in the laminated safety glass.
Processes for making laminated decorative glass have been disclosed in WO 02/18154A1, DE 29706880, U.S. Pat. No. 4,968,553, U.S. Pat. No. 5,914,178, EP 1129844A1, and DE 20100717. These decorative laminates use PVB, PVB/PET/PVB composites, or EVA (ethylene/vinyl acetate copolymers) as the interlayer. While the resulting decorative safety glass laminates may meet the architectural safety codes, these laminates may not perform well in demanding applications such as those outlined above.
Further many of these references disclose a process for making decorative laminated glass via a silk screening process DE 29706880, U.S. Pat. No. 4,968,553, U.S Pat. No. 5,914,178, EP 1129844A1, and DE20100717). Silk-screening an image onto an interlayer is a very time-consuming and expensive process for making decorative laminated safety glass. Inkjet technology is very flexible; any digital image can be printed onto the substrate. Using ink jet technology to print on flexible interlayers (PVB and polynrethanes) for laminated safety glass has been disclosed in WO 0218154. Several disadvantages of ink jet printing directly on PVB include the fact that all PVB interlayers have a roughened surface pattern (Rz from 30–60 μm), which is present to allow for air to escape during the lamination process as described in U.S. Pat. No. 5,455,103. The rough surface pattern can effect image quality with respect to mottle and resolution. Also, polyvinyl butyral is a viscoelastic polymer, which can lead to poor dimensional stability in the image-bearing interlayer.
Interlayers obtained from an ionomer of an ethylene/methyacrylic acid copolymer are stiff relative to other conventional interlayers, and can have improved dimensional stability relative to PVB, for example. However, the Applicants have found that one problem with printing on a stiff material is that a stiff polymer is not amenable to conventional printing processes. The Applicants have found that the process of ink jet printing on a conventional ionomeric interlayer using a conventional ink jet printer is problematical because an ionomer of ethylene/methyacrylic acid copolymer is not flexible enough to be fed through the ink jet printers.